1. Field of the Invention
This invention relates generally to catheters, and more particularly, to a venous catheter adapted to prevent catheter failure caused by thrombus or fibrin formation at the distal end of the catheter and to prevent microbial infection.
2. Description of Related Art
The use of cuffed tunneled central venous catheters has become widely accepted as a viable option for prolonged temporary vascular access as well as permanent vascular access for hemodialysis. It is estimated that 7 million central venous catheters (CVCs) will be inserted into patients annually in the United States. Unfortunately, the durability of central venous catheters is limited by catheter malfunction, primarily manifested by insufficient flow or total catheter lumina occlusion.
A variety of catheter designs exist on the market. Some catheter designs are simple in nature and have a single lumen that extends through an elongate body, while other designs employ two or three lumens. Each lumen has an opening at, or near, the distal tip of the catheter body. More recently, the focus of catheter design has focused on tip geometries that are supposed to provide lower occlusion rates and higher flow rates. Despite the various existing catheter designs, the primary patency rate has been reported to be a dismal 65% at 1 year and in some institutions as low as 45% at 1 year.
To help prevent occlusion, the current clinical practice is to “lock” catheters with Heparin (5000 U/mL) This practice attempts to create a highly anticoagulant environment within each catheter lumen. This practice has inherent risks of systemic anticoagulation since most catheters can hold at least 3 mL of Heparin resulting in a dosing potential of 15,000 U. Furthermore, despite the high concentration of anticoagulant, central venous catheters are still prone to partial or total occlusion leading to poor or failed dialysis.
Failure of hemodialysis catheter patency often results from the accumulation of obstructing thrombus or fibrin at the distal tip of the catheter. Fibrin accumulation may cause failure of smaller single-, double- and triple lumen central venous catheters, but the problem is more significant with hemodialysis catheters, because even partial encroachment of fibrin on the catheter lumen can prevent the high flow rates required for satisfactory hemodialysis. Instillation of Urokinase or tPA into each catheter lumen for thirty minutes in the hemodialysis unit may restore patency to the catheter by lysing thrombosis at the catheter tip, but the effect is often transient or ineffective. No current consensus exists as to what further method is optimal for maintaining catheter patency in patients with regard to catheter failure caused by fibrin sheath formation.
It is also believed that poor catheter position or catheter kinking may also be partially responsible for the low patency rates.
A serious complication that may arise with the use of catheters is infection caused by microbial colonization on the catheter. Even using the best available aseptic techniques during insertion and maintenance of the catheter, one out of every twenty CVCs inserted will be associated with at least one episode of blood stream infection. As a result, it is estimated that more than 300,000 episodes of CVC-related bloodstream infections (CRBSI) will occur annually in the United States. On average, each episode of CRBSI will cost almost $30,000 per survivor and result in an additional average stay of 6.5 days in the ICU.
For long-term catheters, the hub is believed to be a major source of microbial colonization for the catheter lumen, ultimately leading to bloodstream infections through luminal colonization of the intravascular segment.
The surfaces of indwelling medical devices act as a suitable substratum for microbial colonization leading to life threatening infections. Organisms that adhere to the catheter surface maintain themselves by producing a substance rich in exopolysaccharides, often referred to as a fibrous microbial biofilm. The organisms, i.e. bacteria, embed themselves in the biofilm layer, becoming more resistant to the antimicrobial activity of glycopeptide antibiotics. Following catheter insertion, a thrombin sheath rich in host proteins covers the internal and external surface of the catheter. The proteins in the thrombin sheath—such as fibrin, fibrinogen, fibronectin, laminin, thrombospondin, and collagen—act as adhesions. Organisms, such as staphylococci, bind to fibronectin. Staphylococcuss aureus binds strongly to both fibronectin and fibrinogen, while Candida albicans binds well to fibrin. This process observed at the molecular level, is translated into a correlation at the clinical level between thrombogenesis and infection.
In one study, it was determined that catheter related bacteraemia (CRB) is the most significant complication of hemodialysis catheters occurring in 5-18% of catheters or in 3.9-8.6 episodes/1000 catheter days. It is also reported that the cumulative hazard of developing CRB revealed a roughly linear increase in cumulative hazard, suggesting that the risk of developing CRB is constant over time (catheterization days). This suggests that infection is random, there is no threshold effect, and the chance of infection is not related to how long the catheter has been implanted.
Accordingly, it is evident that central venous catheters are plagued with a variety of complications and no existing design has successfully addressed all clinical issues. The most prevalent mechanical complication is occlusion of the distal tip followed by catheter fracture. Although catheter occlusion is not as serious as CRB since it rarely causes death, it does lead to additional non-elective therapies such as tPA instillation and catheter exchange (˜10%). It is evident that the current catheter designs do not provide a reliable means to prevent distal tip thrombosis. In addition, distal tip fouling caused by catheter misplacement, transmural tip incorporation, and external fibrin sheath formation negatively influences catheter performance. Furthermore, microbial colonization on the catheter presents the risk of life-threatening infection.